New owners are often unaware that the contrast control/knob can be pulled into an outer position.
Pushed-in position: The contrast is fixed at a preset value
Pulled-out position: The contrast is adjusted by turning the contrast control/knob
Failure of small-value electrolytic capacitors in the power supply
Premature failure was well known, due to exposure to heat. Of those, my personal notes made in the 80s indicate a common failure of C11 (47µF 35v), but the Internet indicates C13 (10µF 35v) and C14 (1µF 35v) as well.
If you open up the video amplifier cage, you will see that part of the PCB is 'toasted' black. A photo of that is here. It is normal in the 5154, caused by the PCBs long exposure to the heat coming off the high powered resistors (the green things in the photo) and transistors. Because of the heat, expect possible bad solder joints on the legs of the high powered resistors and transistors.
Full or partial vertical collapse
My personal notes made in the 80s indicate that the symptom of full vertical collapse or partial vertical collapse of the raster was somewhat common, and often fixed by replacing the TDA2653A chip. Of course, other causes can result in the same symptoms (e.g. bad solder joints, bad capacitors, ...)
Note that at the rear of the 5154 are two 'vertical size' controls (one for mode 1 operation, and the other for mode 2 operation). So, what may appear to be 'partial vertical collapse' could instead be maladjustment of one of those controls.
1. On the Internet is:
Symptom: Vertical foldover in EGA mode, or incorrect vertical centering.
Replace C311 (100 uf 40v) near vertical amplifier (IC300).
2. Some known electronic component failures are listed in the IBM 5154 section of the database at here.